Also fixes warnings (and bugs) in F4 STM32_USB_OTG_Driver code, allowing -Werror to be enabled for all flight code.
Fixes all other compiler warnings that would otherwise cause the flight code to not compile with -Werror enabled.
Along the way, this also adds some uses of isnan() to various places rather than questionable tests for x != x and
x == x to check for NaNs.
+review OPReview
-Fixed casing for PIOS_BL_HELPER_FLASH_ERASE_BOOTLOADER
-fixed wrong condition in f1 bl_helper
-other cosmetic changes and use of stdbool in f1 pios_bl_helper
-remove now unused macros
+review OPReview-456
